1. Field of the Invention
The present invention relates to a method of fabricating a gate electrode of a semiconductor device, and more particularly, to a method of forming a damascene pattern, in which a metal electrode is fabricated on an upper part of a poly silicon gate so as to prevent a metal electrode from being oxidized when the poly silicon electrode and the metal electrode are formed simultaneously.
2. Discussion of the Related Art
FIG. 1A and FIG. 1B are cross-sectional diagrams describing a method of fabricating a gate formed of a poly silicon and a metal in accordance with the related art.
FIG. 1A is a cross sectional view showing the steps of forming a device separating film 2 on a silicon substrate 1, and sequentially forming a gate oxide film 3, a poly silicon 4, a metal film 5 and a capping film 6 on a front surface thereof, and forming a resist pattern 7 through a photo process.
A gate is formed by carrying out anisotropic etching using the resist pattern as an anisotropic mask as illustrated in FIG. 1B. A high temperature heat treatment of 1000° C. is applied, and an oxide film with a predetermined thickness is formed on a sidewall of the poly silicon. Therefore, an electric field generated on a sidewall member of the gate electrode is reduced such that reliability of a device is increased.
As recognized by the present inventor, the high temperature heat treatment has problems as follows. Since a metal film is oxidized at a relatively high speed compared to a poly silicon film, an oxide film is formed on the sidewall. The oxide film brings an increase of volume in a formative process thereof, and a width of the metal film is decreased, thereby increasing electrical resistance. In the process of ion implantation to be embodied later for forming a source/drain region, the oxide film acts as one kind of mask, reducing an ion-implantation amount at a particular location of a lower part of the oxide film. Therefore, there is a problem that the characteristic performance of a transistor is lowered as well as its yield.